Tests on specimens where specimen contact is undesirable or not possible due to specimen condition or properties.

Deformation measurements on specimens prone to whipping at break which might damage a contact-type measuring system.

Testing possible in temperature chambers and at high temperatures.

Applications requiring biaxial deformation measurement.

With laserXtens high-resolution systems, measurements on small specimen geometries are easy. Flexibility and ease of operation make laserXtens equally suitable for classical quality assurance applications or for use in research and development.

Advantages and features

High precision and resolution

laserXtens possesses high precision in the micro and macro measurement ranges.

Specimens from 1 mm in width/diameter can be tested; smaller specimens may also be possible following pre-testing.

In contrast to contact-type extensometers or pure video instruments, laserXtens can measure strain on short specimens (gage lengths from 1.5mm) with high accuracy.

No specimen contact - no specimen marking

laserXtens has no contact with the specimen; measurement is not influenced by the laser light.

Specimen marks are not required. This saves time, especially with high specimen throughput.

laserXtens can be mounted at varying distances from the specimen. One advantage of this is that it can be used in temperature chambers, where application of gage marks can be very difficult due to environmental conditions.

Easy to use in automated systems also - no manual specimen preparation required.

laserXtens can also measure transverse strain with no need for additional markings; biaxial measurement is possible.

laserXtens is integrated into testXpert III testing software. Use of a separate
monitor is recommended to enable the live image from laserXtens to be observed parallel to
the testXpert III display.

Matrix option allows two-dimensional measurement at up to 100 measuring points distributed arbitrarily or in matrix form over a planar specimen surface. This enables determination of local strains and specimen inhomogeneities.

Another software option allows determination of strain distribution at multiple measuring points along the specimen gage-length. It is also possible to determine strain at break as per Annex H of ISO 6892-1 (laserXtens Compact and laserXtens Array HP only).

Specimen deflection can optionally be deternined in 3 and 4-point flexure tests. Measurement can be carried out at one or three points (with a maximum measurement base of 15 mm).

Specimen range

The following specimen types can be tested using laserXtens:

All types of flat specimens made of plastic and rubber with a thickness of 0.5 to 12 mm

Flat specimens made of metal with a thickness of 0.1 to 30 mm

Round specimens made of metal with a diameter of >1 mm to 30 mm

laserXtens systems consist of measuring heads with digital cameras and laser light sources.The specimen surface is recorded using full-frame digital cameras, while the specimen is illuminated with laser light. The laser light is coherent and dispersed on the specimen surface. This creates a speckled pattern highlighting the specimen surface in the camera image.

The speckled pattern is like a type of fingerprint of the specimen surface. These patterns can be used as virtual gauge marks. Thereby framing areas by evaluation fields and defining the measuring points on which surface movements should be measured.

When a load is applied to the specimen, the virtual gauge marks move. The laserXtens tracks these virtual gauge marks using a highly developed correlation algorithm. This process is known as speckle tracking.

laserXtens' software calculates the strain on the specimen from the relative displacement of the virtual gauge marks and its initial state at the start of the measurement.Two or optionally more virtual gauge marks can be defined in the image, as standard.

Important notes

laserXtens was developed for use with a majority of the classical materials and testing requirements.

Various physical considerations mean that reliable operation of laserXtens requires observance of a greater number of general conditions than when using contact-type extensometers.

The specimen surface must reflect enough laser light to generate sufficiently well-formed speckle patterns. This is the case with most metals and plastics. If necessary simple aids can be used to improve conditions on the specimen surface.

The specimen must be fixed firmly in the center of the test axis in order to minimize movement out of the measurement axis.

All specimen gripping systems which hold the specimen firmly in the center of the test axis are suitable, e.g. hydraulic, pneumatic and screw grips.

In the case of plastics, pre-testing is necessary to determine the reflective properties of the material.

Pre-testing also allows the ZwickRoell Testing Laboratory to assemble the optimum configuration for your particular application. The properties and condition of the specimen surface (reliable measurement signal, resolution), the specimen grips in use (elimination of out-of-plane movement) and the measurement travel required are all checked. ZwickRoell guarantees reliable operation of laserXtens on the basis of pre-tested specimens and testing conditions (= process reliability).

Notes on use with temperature chambers and high-temperature furnaces

When laserXtens HP and laserXtens Array HP are used in conjunction with temperature chambers and high-temperature furnaces it should be noted that the change in optical conditions for testing will have a negative effect on the measurement signal. This basically concerns air currents in the temperature chamber / furnace and outside on the viewing port / furnace port. To minimize these effects the air flow around the specimen must be smoothed and the air currents near the viewing / furnace port minimized by means of optical tunnels. These solutions are designed and produced on a custom basis. Due to the dimensions of the temperature chamber, laserXtens is in this case mounted at a greater distance from the specimen, with consequent changes in resolution and accuracy class (technical details available on request).

laserXtens in Action(3)

1:26

Tensile test on ceramic specimens at high temperature

The laserXtens HT non-contact extensometer was specifically designed for use with high temperature furnaces

1:11

Tensile test on miniature dumbbell specimens made of nickel

The laserXtens non-contact extensometer can measure even strains on short specimens with gage lengths 1.5 mm or higher with great precision.

1:06

Tensile test on an aluminum alloy round specimen

The optical extensometer, laserXtens, does not require contact with the specimen; measurement is not influenced by the laser light.

Technical Overview

laserXtens High Precision

laserXtens HP

laserXtens extensometers for mounting on an AllroundLine testing system

A free slot is required in testControl II.The required INC module is already included in delivery.

Software Options for the laserXtens Extensometer

Strain distribution

The Strain Distribution option enables determination of local strains at multiple
measuring locations along the specimen gage-length. Evaluation of up to 16 measuring locations
is possible. This option also allows automatic real-time symmetrical adjustment of the initial
gage-length around the necking (as per ISO 6892-1, Annex I).

Second measurement axis

This option allows local transverse strain to be measured simultaneously with determination of longitudinal strain.

2D dot matrix

This option allows two-dimensional measurement of dots on a planar specimen surface. This enables determination of local strains and inhomogeneities of the specimen under load. X and Y co-ordinates plus the distances between dots are available as measured values. Up to 100 measurement dots can be measured in any desired arrangement or in matrix
form. Display in testXpert III is limited to 15 channels.

Deflection

laserXtens also determines deflection in 3 or 4-point flexure tests. This can be
measured at one point (displacement of one measurement location) or three points (relative
displacement of the middle or two outer measurement locations) with a maximum measurement base
of 15 mm (20 mm for laserXtens 7-220 HP).

Siemens opts for optical strain measurement by ZwickRoell

Siemens’ customers in the power generation sector have access to a complete spectrum of products, services and solutions for power generation and distribution. Key products in this area include steam turbines and steam-powered generators, together with gas turbines. The high operating temperatures and pressures involved place special demands on materials testing, for which Siemens relies on high-temperature testing solutions by ZwickRoell.